Method of operating an electrolyzer



June 5, 1945. H. 1.; STEWART METHODS OF OPERATING AN ELECIROLYZER s Shets-Sheet 1 Filed Oct. 26, 1940 I Wa M 5 Sheets-Sheet 2 Filed Oct. 26, 1940 H L. STEWART METHODS OF OPERATING AN ELECTROLYZER I June 5, 1945 June 5, 1945. H. 1.. STEWART METHODS OF OPERATING AN ELECTROLYZER 5 Sheets-Sheet 5 Filed Oct. 26, 1940 m 'W M flM.

June 5, 1945. I STEWART 1 2,377,823

' METHODS OF OPERA ING AN ELECTROLYZER Filed Oct. 26, 1940 5 Sheets-Sheet 4 June 5, 1945. H. STEWART 2,377,823

METHODS OF OPERATING AN ELECTROLYZER Filed Oct. 26, 1940 5 Sheet s-Sheet 5 Patented June 5, .1945

METHOD OF OPERATING AN ELECTROLYZER Hubert L. Stewart, Pittsburgh, Pa., assignor, by 'mesne assignments, to Koppel-s Company, Inc.,

a corporation or Delaware Application October 26; 1940, Serial No. 363,029 4 Claims. (01. 204-"80 This invention relates to improved electrolytic means and to methods of operating such means. The invention relates further to improved electrolytic means of a type highly effective in the preparation of useful chemicals and in association with plant units in which such chemicals are employed.

Apparatus for use in the present invention is illustrated in the accompanying drawings in which:

Figure 1 is a diagram of a plant provided with an electrolyzer or cell of thetype hereindescribed, and its associated circulatory system;

Fig. 2 is a detail elevational view of an electrolyzer, employed in 'the above plant, with the various parts in separated relation;

. Fig. 3 is an elevational view of the assembled electrolyzer; I

Fig. 4 is an enlarged view showing in vertical section the various parts in the upper portion of the electrolyzer including assembly means in separated relation;

Figs. 5 and 6 are elevational" views of the outside of the anode end and cathode end respectively of the electrolyzer, with associated channels partly in section;

Fig. 7 is a side elevational view of a. battery of electrolyzers of the type shown in the above figures, and a portion of the circulatory system for generated materials and material to be electrolyzed;

Fig. 8 is a transverse view of the battery on line 8-8 of Fig. '7 in the direction of the arrows; and

Fig. 9 is a fragmentary vertical sectional view of an assembled electrolyzer taken laterally adjacent the near edge shown in Fig. 3, and showing various-parts in place in operative position. Like reference characters are employed to denote similar parts in the several views.

Referring to Fig. 1, the apparatus shown comprises the improved electrolyzer or cell l-for generating carbon dioxide and sodium hydroxide,

and certain plant units associated with said electrolyzer for separating tar acids from hydrocarbon oil. The construction of the electrolyzer will be described first by reierence to Figs. 2 to 5 inclusive, and Fig. 9. I The anode 2 and the cathode 3 of the electrolyzer l are flat plates forming the end walls ofdivides the cell-space into an anclyte chamber or compartment and a catholyte chamber or compartment; and metallic foraminate material which may comprise several layers-in each compartment, such as, a coarse cathode screen I, an anode screen 8 of medium mesh, and fine screens '9 and I0 positioned between the diaphragm and the screens 1 and 8 respectively. The screens 9 and I0 compressively engage opposite sides of the diaphragm. A spacing means ll determines the distance between the electrodes 2 and 3.

The electrolyzer is held together by means of bolts l2 passing at intervals through the electrode plates 2 and 3 adjacent the edges thereof, and through the spacer H and an insulating gasket l3 placed, for instance, between the spacer -II and the electrode 3. To insulate the bolts l2,

an insulating sleeve I4 is positioned in each bolt hole I5 in the electrode 3 and around the bolt l2. The bolt holes IS in the electrode 3 may be enlarged for this purpose. An insulating washer I6 through which the sleeve It extends, a steel distributing washer ll providing uniform pressure over the entire surface of the washer l6, and a nut IB are brought successively over a threaded end IQ of the bolt 12.

When the electrolyzer parts are assembled as in Fig. 3 and Fig. 9 and the nuts IB are tightened,

thevarious elements (including the diaphragm the electrolyzer to which suitable conductors .4

and 5 respectively are connected. in electrical circuit with a source of electric current (not shown). The electrode plates 2 and 3 are spaced apart just enough to house a diaphragm 6 that- 6 and the several screens 1-40) positioned in the electrolyzer, take up preferably substantially the entire cell-space for the purposes hereinbelow indicated.

Means are provided whereby anclyte solution and catholyte solution may be separately with- .drawn and whereby improved controlled circulation may be obtained in the anolyte chamber and in the catholyte chamber of the electrolyzer. Passage means integrally associated with the anode 2 and with the cathode 3 serve as conduits for introducing or withdrawing various media. Such-passage means (described below) are conveniently provided by welding the edges of channel irons onto the outer sides of the electrodes 2 and 3.

-As shown in Figs. 5 and 6 as well as in Figs. 2-4, ports 25 and 26 are provided in the anode 2 near the top and bottom respectively of the anolyte chamber of the electrolyzer, and ports 21 and 28 are provided in the cathode 3 near the top and bottom respectively of the catholyte chamber. These ports are preferably uniformly spaced at the respective levels-in a horizontal plane across each electrode face.

Connecting the upper ports in the upper level of the anode is a passage 29 formed by a channel iron 30 closed at its ends. Similarly a passage 3| formed by a channel iron 32 connects the lower ports 26 of the anode; a passage 33 formed by a channel iron 34 connects the upper.

ports 21 of the cathode; and a passage 35 formed by a channel iron 36 connects the lower port 28 of the cathode,

As distinct from the anode 2, the cathode 3 has attached thereto additional channel iron 31 spaced apart and placed vertically to form a plurality of passages 38 that connect the passages 33 and 35.

For purposes to be set forth in the description of the operation of the electrolyzer, pipes 40 and 4| are connected to the passage 29, a plurality of the pipes 40 being properly spaced and extending upwardlyfrom the upper wall of the channel iron 30, and a plurality of the pipes 4| being likewise properly spaced but extending outwardly from the vertical wall of the channel iron 30. A plurality of spaced pipes 42 extend outwardly from the vertical wall of the channel iron 32 and are connected to the passage 3 A plurality of spaced pipes 43 and 44 are connected to the passage 33, the pipes 43 extending upwardly from the upper wall of the channel iron 34 and the pipes 44 extending outwardly from the vertical wall of the channel iron 34. outwardly from the vertical wall of the channel iron 36 and are connected to the passage 35. A closed pipe 46 for conducting a fluid for controlling the temperature of an electrolyte solution extends longitudinally through the passage 3| formed by the channel iron 32 at the lower level on the anode 2.

The several pipes 4|, 42, 44 and open into the respective passages at levels below the ports 25, 26, 21 and 28 respectively, thus providing traps i for liquid to prevent escape of gases.

In Fig. 1, the cell I is shown diagrammatically in its relation to circulatory means for anolyte and catholyte products. Also, its adaptation to a tar acid plant is illustrated in this figure. One of each of the pipes 40, 4|, 42, 43, 44 and 45 and their separate connections are shown inFig. 1. It is readily seen that one or a plurality of each of such pipes can be used and that pipes corresponding respectively to each of these can be connected in a similar manner. .The pipes 4| and 42 are connected to an electrolyte feed main 50. The pipe 44 is connected to a trap such as that designated by the numeral 5| and the pipe 45 provided with a valve 52 is connected to a supply main 53 for liquid. The pipe 40 is connected to a pipe 54 opening into the-upper side of the main 50, and pipes 40 and 54 are connected to a gas main 55. The pipe 43 is connected to a gas main 56. The pipe 46 provided with a valve 51 is connected to a supply main 58 for conveying a heating fluid.

For electrically insulating the cell, the various pipe connections thereto may be provided with proper insulating means, or the pipe sections attached to the cell may be made of insulating material, as is readily understood.

In the operation of the cell for generation of sodium hydroxide and carbon dioxide for use intar acid production, sodium carbonate solution, for instance, from the feed main 5!! passes into the anolyte chamber through the pipe 42. The level of the solution in the. anolyte chamber is brought to slightly below the levels 01' the ports 25 or the pipe 4|. Water from the supply main A plurality of spaced pipes 45 extend 53 is slowly admitted through the pipe 45 into the catholyte chamber and the electric current in the cell circuit is turned on.

By properly positioning the various pipes connected to the anolyte chamber of the cell, circulation of sodium carbonate solution in said chamber may be constantly maintained during electrolysis without the use of a pump or similar device ordinarily employed for transferring liquids. To accomplish this, the main placed horizontally and serving as a reservoir is positioned so that the level of solution 60 therein can be maintained at the level of or just below the level of the opening of pipe 4| into the side of the main 50, the pipe 4| extending horizontally from the passage 29 within the channel 30 to the main 50. The pipe 42 opening into the bottom of the main 50 extendsdownwardly from the latter to the passage formed by the channel 32.

While electrolysis proceeds, the buoyant effect of evolved gases within the restricted space in each of the relativel narrow compartments of the cell causes circulation in each compartment to be maintained. The liquid in the anolyte compartment and the liquid in the catholyte compartmerit are separately repeatedly circulated in the respective compartments. As generated gases, carbon dioxide and oxygen,'rise in the anolyte chamber, liquid and these gases pass through the ports 25 into the passage 29. The gases separate from the liquid and pass through the pipe 40 into the main 55. The liquid overflows from the pass ge 29 into the main 50. Any gas that passes into the main 50 with the liquid is conveyed by means of pipe 54 into the main 55. Liquid withdrawn from the upper zone in the anolyte chamber is continuously and automatically replaced by liquid coming from the main 50 through the pipe 42 and flowing into the bottom of the anolyte chamber through the ports 26. The main 50 may serve simultaneously as an electrolyte reservoir and as a gas collecting main.

The gas from the anode chamber of the cell l is led through a pressure control means 55 of well-known construction, whereby pressure in the anode chamber may be raised to any desired height and whereby the amount of solution passing through the diaphragm may be directly controlled. With dense diaphragms higher pressures are required than with those less dense. At higher pressures it is found that product rate can be more effectively controlled.

In the catholyte chamber, in which hydrogen is generated, the buoyant effect of this gas causes the liquid to rise and to flow through'the port 21 into the passage 33 formed by the channel 34.

The hydrogen separates from the liquid and passes upwardly through the pipe 43 into the collecting main 56. The liquid passes downwardly through vertical passages 31, into the passage formed by the channel 36, through the'ports 28 and back into the catholyte chamber. Liquid from the passage 33 also overflows into the pipe 44 and into the trap 5| from whence it passes into a catch-all 65 connected to the intake of a pump 66.

During electrolysis, a supply of sodium carbonate solution is maintained in the main 50. A concentration of sodium carbonate supplied, that gives highly satisfactory results, is from about t 230 grams perliter of water. Concentrations above and below this range may be used. as for instance, 10 to 25 per cent solutions of sodium carbonate. The strength of the sodium carbonate solution depends to a certain extent on and other factors.

the strength of sodium hydroxide solution de-- sired.

The cell temperature is preferably not below 100 C. nor much higher than 105 C. To maintain these temperatures, steam or other heating fluids are passed through the pipe 46 preferably 'closed for indirect heating in the passage 3 I. The temperature may be effectively controlled by means of the valve 51.

The cellvoltage during electrolysis is, by way of example, preferably between about 2.65 volts 4 and about 3.6 volts. These voltages depend largely on the temperature of the cell, polarization, A current density of 125 am peres per square foot has been found effective.

In the electrolysis of sodium carbonate solution, the sodium carbonate dissociates as follows In view of the temperature of the anolyte chamber, the carbonic acid (H2003) that forms therein does not react with the sodium carbonate phragm between the electrodes 2 and 3 may pref.

to form sodium bicarbonate. Instead, carbon dioxide (002) is liberated and this gas mixed with oxygen (02) that is also liberated in the anolyte chamber, passes into the main 55. The mixture of gas is found to contain from about 50% to about 60% carbon dioxide and about 40% to 50% oxygen. I

As indicated above complete circulation is maintained within the cell by the evolved gases.

Uniform distribution of ions is maintained in the anode chamber while sodium hydroxide is removed from the cathode chamber as it is formed.

Water is preferably continuously introduced into the catholyte chamber from the main 53 and its rate of introduction is controlled by means of the valve 52. While the catholyte liquid is automatically passed in a cyclic path in and out of the cathode chamber, thereby avoiding stratification, the water from the main 53 is, in general, admitted into the path of the circulating liquid at such a rate as to produce sodium hydroxide solution of the desired concentration. The concentration of the sodium hydroxide solution withdrawn through the pipe 44 may be in the range of about 10% to or A con- 9 version ofiabout 75% to 85% is realizedin the use of the cell. The gas coming from the catholyte chamber and passing into the main 56 contains about 98% to 99.5% hydrogen.

Highly satisfactory results have been obtained byintroducing water into the catholyte chamber at a rate that prevents the sodium ion concentration in the catholyte chamber from exceeding the sodium ion concentration in the anolyte chamber by more than about ten per cent. This may be varied over a substantial range above or below the excess of ten per cent. Osmotic action through the diaphragm is thereby effectively prevented or reduced. I

To prevent OH- ion diff on, the diaphragm may be constructed of a uniform mixture of asbestos fiber and calciunicarbonate (CaCOa). About 8% calcium carbonate and about 92% asbestos fiber give highly desirable results. These proportions may be varied, namely, the asbestos {fiber between 50 and 95%, and the calcium carbonate een 50 and 5%. In making a diahragm he cell, the anode section 2 with the spacing means II is placed in a horizontal position. The coars screen 8 and the fine screen Ill are put in place within the spacing means, and a wet mixture of calcium carbonate and asbestos erably be avoided.

It is believed that due to the presence of calcium carbonate in the above type of diaphragm, the cell produces higher caustic concentrations at higher conversions and with lower voltage than other types of electrolytic caustic cells. It may be assumed for instance that the following reaction is reversible and is not a'quantitative one:

It is noted that the calcium carbonate, in the body of the diaphragm, upon conversion into calcium hydroxide absorbs some of the OH ions, and therefore the migration thereof through to the anode is greatly reduced. In other words the diaphragm acts as a hydroxyl reservoir, taking up excesses of hydroxyl ions when they exist and releasing them to react with sodium as sodium carbonate is forced through the diaphragm from the anode side.

Relative to the screens I, 8, 9 and ID in the cell, it is noted that these may vary in the size of their meshes and of their wires. By way of example, satisfactory results have been obtained by using the following screens:

Screen Mesh Wire size 1% inches to 3% 0.25

inches. 34 inch to 2 inches... 0.20 No. 22 0.08 N0. 11 0. 08

Besides aiding in liquid circulation, the screens the finer screens 9 and ID are in contact with the screens and 8 respectively. Contact between screens and 9, and between 8 and I0 is established by the pressure exerted by the diaphragm, or in other words the screens 9 and I0 serve as compression contact means.

The screen Ill presents the active surface for the anode. It is preferably a little coarser than the screen 9 for the reason that sodium bicarbonate has a tendency to form in the anolyte chamber and to clog the meshes. With the larger meshes, there is less tendency for clogging. Besides, as previously indicated, the operation of the cell at the. temperatures mentioned prevents settling of salts. 7

The screen 9 is the active surface at which sodium hydroxide is formed. Due to movements set up in the liquid in the catholyte chamber, the

sodium hydroxide is carried away from the diaphragm immediately upon formation in a direction toward the openings 21.

Since the carbonate ion is slower in its migration-than the sodium ion, the speed of migration ,of the carbonate ion may be increased by having screen 8 less coarse than screen I, thereby pro- A diaphragm of uniform thickness tively small quantities of solution are required to fill the electrolyzer. Owing to the small amount of solution present in each electrode chamber, large quantities of solution are readily and easily recirculated by the buoyant effect of the evolved gases.

By means of the above-described electrolyzer, which may be constructed entirely of steel, a highly improved anolyte and catholyte circulation is provided, with effective control over ion concentrations, complete control over cathode alkali, and positive cell temperature control in the higher ranges. Increased operating economies under improved voltage conditions and with improvement in quality and yields of sodium hydroxide are realized. By the use of the particular diaphragm effective control of the OH ion is exercised, and plugging of the diaphragm I a is considerably reduced due to reduction in the quantity of electrolyte passing through.

Furthermore, the electrolyzer is particularly suited for the generation of sodium hydroxide solutions of desirable concentrations for extraction of tar acids as sodium phenolate and for the generation of carbon dioxide for springing the phenolate. Due to the small floor space required, housing costs for a plant of a given capacity are greatly lowered.

'In Fig. '7, a plurality of electrolyzers l are shown with conduit connections for generation of the various products. The electrolyzers may be electrically, connected in series, and provision may be made for electrically insulating the various conduit connections from the electrolyzers. Parts of the apparatus shown in Fig. 7 that correspond to parts shown in Fig. 1 and subsequent figures are designated by the same numerals.

Each electrolyzer l is connected to the reservoir and gas collecting main 58 by means of the anolyte circulating conduits II and 42 leading from the channel 3|] and 32 respectively. A pipe 48' for conducting gas from the anolyte chamber of each electrolyzer is also connected to the channel and to the main 58. A main 55" may be connected to the main 50 for drawing gases from the latter for use. If desired, pressure control means similar to means (Fig. 1) may be provided in the main 55", whereby release of generated gas from the anolyte chamber is permitted and yet sufiicient pressure is pro vided to force the liquid from the main 50 into the anolyte chamber of each cell and through the diaphragms at the proper rate. The main 50, which is kept partly filled with solution to be electrolyzed, may be extended to supply any desired number of electrolyzers with sodium carbonate solution or other solution to be electrolyzed, such as, potassium carbonate or sodium sulphate solutions.

' Steam for heating the anolyte solution is conducted from .the main 58 through pipes 46' each provided with a valve 51', the said pipes 46 passformity in production particularly with respect to the catholyte solution.

Solution from the catholyte chamber of each cell is withdrawn through pipes 44' from the channels 34 and is passed into a main Hi from whence the solution iswithdrawn for use through a trap l I. Pet cocks (not shown) for sampling the oatholyte solution from each cell may be provided in each of the pipes 44. Gas from the catholyte chamber of each cell is withdrawn through pipes 43 connected to the channels 34 and to the main 56.

As set forth above, the products obtained from the battery in the electrolysis of sodium carbonate solution are sodium hydroxide solution in the main 10, carbon dioxide and oxygen in the main 55", and hydrogen in the main 56.

In a tar acid plant as shown in Fig, 1, the sodium hydroxide solution produced from sodium carbonate solution in the above electrolytic means, at the desired concentration by controlling the flow of solvent or dilution water into the oatholyte chamber of an electrolyzer, is employed for the extraction of phenolic bodiesfrom' tars and oils containing the same, thereby converting the phenolic bodies to their corresponding sodium compounds. The carbon dioxide released from the anolyte chamber at the operating pressures is employed to spring the sodium compounds to free the phenol or tar acids, thereby reforming sodium carbonate solution which is returned to the supply main 50 and the electrolyzer for generating sodium hydroxide and carbon dioxide.

The terms phenolic bodies" or pheno are employed herein in their broad sense, and include hydroxylated benzenoid substance in general as well as benzophenol (carbolic acid, CeHsOI-I) specifically. Phenolate" is used to designate a salt of the so-called phenols or in other words phenols combined with the positive radical of a base. Besides benzophenol other specific phenols are, for instance, the cresols, xylols, naphthols and various substituted phenols. The raw material used as a source of phenol may be various tars and oils from coal or petroleum, or other phenol-bearing material.

The phenol-bearing material such as tar acid oil is passed into the bottom of a column 15 through an inlet pipe 16, its rate of flow being controlled by a valve ll. Sodium hydroxide solution maintained at a, concentration preferably between 12 and 15% is pumped by means of the pump 66 from the electrolyzers through a pipe 18 into the top of the column 15. The interior of this column may be provided with well-known baiile means such as bell and tray or other means. Thecaustic solution and the tar acid oil pass through the column l5 countercurrently. The oil or so-called neutral oil from which phenol has been removed passes out near the top of the column through a pipe 19 provided with a valve 80. The sodium phenolate solution is removed at the bottom of the column 15 through a pipe BI and is subsequently treated to spring the phenolate.

Before springing, the phenolate solution removed from the column 15 is preferably passed throughthe pipe Bl into an evaporator 82. Steam or other fluid for heating the evaporator is introduced through a pipe 83 having a valve 84. The evaporation may, if desired, be conducted under vacuum and also with live steam in either or both direct or indirect contact. The concentrated phenolate is passed through a pipe 85 from the ggaporator 82 into the top of a springing column To spring the phenolate introduced into the column 86, carbon dioxide gas at a predetermined pressure and rate is passed through the pipe 55 from the electrolyzers into the bottom of the column 88 having baflle means therein of wellknown construction, as for instance, belland tray means. The gas and phenolate pass countercurrently throughthe column 86. The phenolate in column 86 is reacted upon by the carbon dioxide to form free phenol and alkali carbonate. The

free phenol is removed from the springing column through a pipe 81 and is passed into a decanter 88,

from the upper level of which it is withdrawn through a pipe 89.

The alkali carbonate solution is removed from the bottom of the springing column 86 and from the bottom or the decanter 88 through a T-connection provided with valves 90, 9i and 92. The

carbonate solution is then passed through a pipe 88 into an evaporator 94 similar in its equipment and construction to the evaporator 82. Steam or other heating fluid is introduced through a pipe 85 having a valve 96. Any free phenol separated from the carbonate solution during heating is passed from the evaporator 94 through a pipe 91 2 into the top of the entraction column .ibfii hereformed carbonate solution is passed into a storage tank 98 and before passing it into the main 58 through pipe 99 it is preferably filtered in a nlter m (Fig. 1) or llill (Fig. 7)

The pipe 65 for conducting carbon dioxide to the springer 88 may be provided with a bypass pipe ilii to avoid connection with a carbon dioxide generator I02, such as a coke burner, which voltage, the kwh. reguired per pound of caustic produced is relatively low.

Reference is made herein to Patent No. 2,172,- 415 dated Sept. 12, 1939; issued to Hubert L. Stewart and to applications of the latter, namely, Serial No. 87,569, filed June 26, 1936. and Serial No. 251,412, filed January 17, 1939. Patent NO.

2,172,415 is directed to a process of recovering phenols in which alkali bicarbonate and alkali hydroxide prepared electrolytically are employedas reagents. Application Serial No. 87,569 describes improvements in electrolytic cells or the filter-press type and methods or operating the same to produce chemicals such as alkali bicarbonate and alkali hydroxide. Application Serial No. 251,412 discloses and'claims a hori- Iontal type of cell, circulatory means ior anolyte solution, and methods or operating such cell and 4 means to produce chemicals, such as, alkali bicarbonate and alkali hydroxide.

What is claimed is: V 1. A method of operating an electrolyzer, comprising separately circulating normal alkali car-.

bonate solution through the. anolyte chamber of 5 an electrolytic diaphragm cell while electrolyzing the solution and while applying heat to the solution in the anolyte chamber and maintaining it not insald chamber to separate therelrom carbon dloxlde as a product, separately introducing water 0 into the catllolyte chamber or the cell to thereby dissolve in said water an alkali hydroxide catholyte product generated lrom the said solution, and withdrawing alkali hydroxide solution and carbon dioxide rrom the said cell.

2. in a method or operating an electrolyzer to prepare alkali hydroxide and carbon dioxi e by electrolysis of normal alkali carbonate solution, wnlle separately circulating normal alkali carbonate solution through the anolyte compartment the said solution while mamtalnmg the temperature or the solution in said compartment between 100 C. and 1ub C.-to obtain carbon dioxide gas and to prevent formation or bicarbonate in the 5 anolyte solution, and separately introducing waterifito tfiecatholyte. compartment or the cell to form alkali hydroxide solution as an electrolysls product, and withdrawing carbon dioxide from the anolyte compartment and so-iormed 3 alkali hydroxide solution i'rom circulation.

3. In a method of operating an electrolyzer to prepare alkali hydroxide and carbon dioxide by electrolysis of normal alkali carbonate solution, while separately passing normal alkali carbonate solution in a cycle repeatedly into and out of the anolyte compartment of an electrolytic diaphragm cell, electrolyzing the said solution while maintaining it hot in said compartment to obtain carbon dioxide gas, introducing water into the catholyte compartment of the cell to form alkali hydroxide solution, and during the electrolysis passing the resulting catholyte solution in a separate cycle repeatedly into and out of the said catholyte compartment to thereby obtain a solution of alkali hydroxide, and withdrawing so-iormed carbon dioxide gas from the anolyte solution cycle and alkali hydroxide solution from the said separate catholyte solution cycle.

4. A method or operating an electrolyrer, comprising separately cycllcly circulating normal alkali carbonate solution through the anolyte compartment of an electrolytic diaphragm cell while electrolyzing the said solution and maintaining it hot in said anolyte compartment: and

during the electrolysis introducing water into a catholyte solution cycle in which said catholyte solution is separately cycllcly circulated through the catholyte compartment of the said cell and in which the said water is mixed with generated alkali hydroxide cathclyte material to form the catholyte solution, and seperately withdrawing so-iormed alkali hydroxide catholyte solution from the said cell.

HUBERT I. STEWART. 

